OpenGL 4.3 Specification Also Released

Alongside OpenGL ES 3.0, desktop OpenGL is also being iterated upon today with the launch of OpenGL 4.3. Unlike OpenGL ES this is only a much smaller point update. This is not to say that it’s unimportant, but it will bring a smaller list of new features to the table.

At the same time though, this also marks what may potentially be an interesting inflection point for OpenGL gaming on the desktop. On Windows OpenGL usage has never been lower; the only AAA game engine still based on OpenGL is id Tech 5, which with the termination of licensing by id is only used internally. Khronos of course would like to change that, so when Valve Software says that they’re going to be porting Source over to Linux (thereby increasing the audience for OpenGL games) it’s of quite some interest to Khronos. At the same time desktop OpenGL still has a long way to go to recapture its glory days in the late 90’s and early 2000’s, so Khronos is doing what they can to spur that on.

OpenGL ES 3.0 Superset & ETC Texture Compression

Moving on to looking at OpenGL 4.3’s features, unsurprisingly, one of the big additions to OpenGL 4.3 is to add the necessary features to make it a proper superset of OpenGL ES 3.0. One of Khronos’s missteps with OpenGL ES 2.0 was that it wasn’t until OpenGL 4.1 in 2010 that desktop OpenGL become a proper superset of OpenGL ES 2.0, which they’re rectifying this time around by launching OpenGL ES and its equivalent OpenGL at the same time.

Because OpenGL ES 3.0 is largely taken from desktop OpenGL in the first place, there aren’t a ton of changes due to this. But there is one: texture compression. The aforementioned standardization around ETC applies to both OpenGL ES and OpenGL, which means that starting with OpenGL 4.3, desktop OpenGL will have a standard texture compression format.

Practically speaking, this won’t make a huge difference to desktop developers right now. Because S3TC is a required part of the Direct3D specification and all desktop GPUs support Direct3D, S3TC has been a de-facto OpenGL standard for nearly 10 years now. And because few developers will target OpenGL 4.3 right away, that won’t change. But this means that developers targeting 4.3 do finally have a choice in texture compression, and developers doing cross-platform development with OpenGL ES can use the same texture compression format in both cases.

It’s worth noting though that just because a GPU “supports” ETC doesn’t mean it has hardware support. NVIDIA has told us that they’ll be 4.3 compliant, but they’re handling ETC by decompressing the texture in their drivers before sending it over to the GPU in an uncompressed format, and while AMD wasn’t able to get back to us in time it’s almost certainly the same story over there. For ports of OpenGL ES games this isn’t going to be a problem (dGPUs have plenty of high-bandwidth memory), but it means S3TC will remain the de-facto standard desktop OpenGL texture compression format for now.

OpenGL Compute Shaders

Moving on, while OpenGL ES 3.0 compatibility is a big deal for OpenGL, it’s actually not the biggest feature addition for OpenGL 4.3. For that we turn to compute shaders.

As a bit of background, when meaningful compute functionality was introduced for GPUs, Microsoft and Khronos went in two separate directions. Khronos of course created OpenCL, a full-featured ANSI C based API for compute. Microsoft on the other hand introduced compute shaders, which was a special class of HLSL designed for compute. OpenCL is far more flexible, but flexibility has its price. Specifically, implementing compute functionality in OpenGL games often wasn’t as easy as the equivalent functionality using a Direct3D compute shader, and the overhead of OpenCL limited performance.

The end result is that Khronos has decided to implement compute shaders in OpenGL in order to bridge this gap. OpenCL of course remains as Khronos’s premiere compute API for both stand-alone compute applications and OpenGL games/applications that need the full flexibility, for but games that don’t need that level of flexibility and only want to run compute work on a GPU there is now another option.

Like Direct3D’s compute shader functionality, OpenGL’s compute shader functionality is geared towards relatively simple pixel operations, where approaching an algorithm in a compute manner (instead of a graphics manner) allows for faster execution. The compute shaders themselves will be written in GLSL rather than C, underscoring the fact that this is an extension of OpenGL’s shading framework rather than their compute framework. The target for this functionality will be games and other applications which perform compute “close to the pixel”, taking advantage of the faster shared memory and greater thread count that compute shaders offer.

Since OpenGL’s compute shader functionality is being spurred on by Direct3D, it should come as no surprise that OpenGL’s compute shaders are going to be a very close implementation of Direct3D’s compute shaders. Specifically, OpenGL’s compute shader functionality is being advertised by Khronos as matching D3D11’s compute shader functionality. The differences between HLSL and GLSL mean that there’s no straightforward portability, but it underscores the fact that this is the OpenGL analog of D3D’s compute shader functionality.

New Texture & Buffer Features

Moving on, OpenGL 4.3 will also be introducing some new texture and buffer features. On the texture side of things, one new feature will be texture views, which allow for a texture to be “viewed” in a different way by interpreting its results in a different manner, all without needing to duplicate the texture for modification. As for buffers, 4.3 introduces support for reading and writing to very large buffers across all shader types and all stages. The idea behind this is that it’s an efficient way for those new compute shaders to communicate with the graphics pipeline, given the large amount of data that can be in flight with a compute shader.

Wrapping things up, for some time now Khronos has been working on bringing OpenGL into alignment with Direct3D in order to close the feature and developer gap that has been created between the two. As Khronos correctly notes, with the addition of compute shader functionality OpenGL is now a true superset of Direct3D. If desktop OpenGL is going to see a resurgence in the next few years, it’s now in a far better position to pull that off than it was in before.

What’s New in OpenGL ES 3.0 Adaptive Scalable Texture Compression
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  • BenchPress - Monday, August 06, 2012 - link

    S3TC support is not demanded. You can query which formats are supported, and trying to create unsupported ones will fail.

    Of course texture compression is important so the major hardware manufacturers implemented it and pay for it. But this is equally true for OpenGL. They all implement the extension.

    Core Direct3D functionality is royalty free, just like OpenGL. After all, they are just APIs.
    Reply
  • mczak - Monday, August 06, 2012 - link

    That isn't quite true for DX10 and up. There's very few optional formats, almost everything is mandatory (including the s3tc formats).
    That said, IIRC hw manufacturers did NOT have to pay s3tc license fees due to some licensing deal of MS (if they implemented s3tc for d3d, they still had to pay for OGL).
    Reply
  • StevoLincolnite - Monday, August 06, 2012 - link

    Direct X is also used on the Xbox 360 which is a games console, the PS3 even has Direct X 9 hardware, albeit without the API. (It uses OpenGL)
    Android, iOS and other mobile OS's can't play AAA games like a PC or Console can, in-fact most games are incredibly simple with decade old level of graphics.

    Steam has what, 30-40 million users? Origin is picking up steam (Pun intended), Ubisoft uPlay probably has a few users.

    So lets go with 40 million PC gamers (Which is probably lower than the true number.) which in turn use Direct X.
    Then add on the Xbox console numbers which makes it 110 million gamers that use Direct X in one form of another.

    Suddenly Direct X doesn't look insignificant.

    If you go back almost a couple decades during the Era of 3dfx, Allot of games actually used multiple API's that you could choose depending on your hardware.
    I remember Unreal Tournament for instance coming with 3dfx Glide, OpenGL, Software Rendering and Direct 3D, so it's not like you can't support multiple API's in a game engine using some wrappers, which may be the path developers may take in the future again.
    Reply
  • BiggieShady - Monday, August 06, 2012 - link

    Saying things like "PS3 has DX9 hardware but it uses OpenGL" is wrong on so many levels. DirectX and OpenGL are API-s designed to work with different types of hardware with one thing in common - they expose the same hardware functionality. So PS3 and Xbox have different GPU-s that both expose same functionality either for OpenGL or DirectX. Reply
  • wicketr - Monday, August 06, 2012 - link

    There are over 500 Million Mac/Linux/Smartphone/Tablet users that DirectX isn't on. Meaning that a developer using DirectX would miss out on those users.

    ....Or they could use OpenGL and cover 100% of the user base. Currently, it'd be asinine to develop a mobile only game in DirectX, because they'd only reach about 5% of the market.

    The question on the desktop is if DirectX's feature set is THAT much better than OpenGL to warrant it's use. As OpenGL catches up in parity and as more users abandon Windows, the reasoning for using DirectX gets smaller and smaller, especially as developers get more and more comfortable in OpenGL (due to mobile programming).

    The only way DirectX can really survive over the long term (10+ years out), is if Microsoft develops engines compatible for iPhone and Android. Those ecosystems are just WAY to large for Microsoft to use their proprietary engine to push users (and developers) to MS Phones.
    Reply
  • bobvodka - Monday, August 06, 2012 - link

    DX will survive as long as there is a Windows or XBox market for it to survive in.

    Beyond that developers, like myself, will do what we've always done and use the best API for the target platform.

    Amusingly the only people who really seem to care about which API 'wins' are OS Zealots who want their OS to dominate the world... which, you know, works so well...

    The rest of us doing the real work day in-day out will just use the best tools for the job and won't care who they come from.

    Unfortunately, right now, the ARB doesn't have a track record of 'the best tools' having dropped the ball with the Longs Peak/OGL3.0 debarcle which was, at the time, OpenGL's best chance of 'making a come back' on Windows (this was around the time of Vista/DX10 and the wailing of XP gamers who wanted DX10 features in their games) - when it comes to OpenGL I wouldn't trust the ARB to find their own arses if handed a map.

    Now, OpenGL|ES is another matter, they have handle that well and its a good thing BUT OpenGL|ES is NOT OpenGL (yay marketing!); you do not program these APIs the same way and doing so is going to hurt you which brings us back around to 'the right tools for the job'.

    OpenGL is not, for the majority of the home computer market, the right tool yet.
    Reply
  • ananduser - Tuesday, August 07, 2012 - link

    The user to which you replied presented some vague numbers representing dedicated gamers and not the install base. You counter that with the totality of non-Win devices ?

    You seem bent on people "abandoning" Windows like it's the plague and it's the right thing to do. You also seem to go to sleep at night wishing DirectX was dead so that EA would develop BF4 for your mac(I presume).

    DX will still be the dominant gaming industry API even 10 years out. Even more so than today.
    Reply
  • SleepyFE - Monday, August 06, 2012 - link

    DirectX is being used because people think like you (and so far it was better). Most people use Windows so why not use DirectX. NOW you have 110 mill gamers using DirectX because developers used it. If they decided to use OpenGL which also works on Windows and Xbox you would have 110 mill gamers using OpenGL and a few million using DirectX because Microsoft was the developer's partner and they forced them to use it.

    So far using OpenGL was a problem since it had less features and was harder to learn (deep end of the pool). Now is the time to make the switch.

    Also, i do not use Windows because i like it, i like the games that are made for it. If i want to play a game, i am FORCED to have Windows because of DirectX only running on Windows. Using OpenGL does not yet mean it will run everywhere, but it does mean a lot less work to get it working elsewhere. Right now so many people are on Windows that developing the game in both DirectX and OpenGL just doesn't pay. Using only one is the way to go. An OpenGL title right now has a slightly wider audience (a very very very very small increase). But if they keep using DirectX we have to keep using Windows (even if we don't like it).

    Games are the reason most of us use Windows, but with good OpanGL that might change. Ouya is a gaming console with Android and as phones become more and more powerful we might only need a phone some day. A phone with a super fast USB 5.0 that is plugged in to a monitor with more USB ports for a keyboard, mouse, controller... And that phone will probably have Android on it. And to play games you will need OpanGL. At that point it would be good to have a huge selection of games (even if they are old and outdated, nostalgia never goes out of fashion).
    Reply
  • bobvodka - Monday, August 06, 2012 - link

    The PS3 does not use OpenGL.

    There is a PSGL implimentation but no one who wants any speed out of the thing uses it; GCM is the PS3 API of choice.

    Linux and OSX are the only OSes which use OpenGL exclusively.

    Mobile devices use OpenGL|ES which is a different API completely and, more importantly, can not be used in the same manner as OpenGL. They are moving closer in feature parity however even then I would call anyone who treated a mobile device like a desktop insane.

    Developers also regularly support multi rendering APIs when they produce 360, PS3 and PC titles; right now we (where I work) are producing a game which has support for X360, PS3, D3D11 and early WiiU support.

    In the future, for a short while at least until we can drop it for the older platforms anyway, I suspect we'll have X360, PS3, D3D11, XBox720, PS4, WiiU and iOS support in the renderer (maybe Android too, although I know of no plans personally) - as always we will pick the best API for the platform.
    Reply
  • wicketr - Monday, August 06, 2012 - link

    The question is what API are you using for Mac users? They are 10% of desktop users, and significantly more than that if you discount the business segment of computers. Surely you're not ignoring a fourth (and growing) of the consumer desktop/laptop market by not even writing your game for Macs.

    If it's OpenGL, then wouldn't it be a greater benefit to "write once, deploy twice" on both OSes? Or are the graphical benefits of DirectX really that much better to write it twice?
    Reply

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